1. Field of the Invention
The present invention relates to a portable electronic apparatus having a secondary battery therein, the secondary battery being a battery that can be charged, and also relates to a charging apparatus for the portable electronic apparatus.
2. Description of the Related Art
A portable electronic apparatus such as a portable phone terminal has a secondary battery therein, the secondary battery being a battery that can be charged using an external power supply. Regarding a charging control device for such a secondary battery, a technology for accurately controlling a charging voltage and detecting a charging current while suppressing heat generation during charging has been suggested (see Japanese Unexamined Patent Application Publication No. 2008-104270).
In order to increase charging efficiency during charging of a secondary battery, the following method is adopted. That is, a power supply voltage supplied from the outside to a charging integrated circuit (charging IC) is decreased by a direct current-direct current (DC-DC) converter and is supplied to a power supply IC, and the secondary battery is charged.
With this method, power can be supplied from the secondary battery when it becomes necessary for the power supply IC to supply a current beyond the ability of power supplied from the outside. For this purpose, a rapid fluctuation of load is detected on the basis of a fluctuation of the voltage of supplied power having a decreased voltage and a result of a current monitor by using a so-called battery assist function, and a power supply path is switched by using a switch, such as a field-effect transistor (FET).
FIG. 1 illustrates a configuration of a charging system in a portable phone terminal according to the related art.
A power supply IC 104 supplies power to devices, such as a baseband (BB) IC 100 including a communication unit and a central processing unit (CPU), a peripheral device 102 such as a liquid crystal display (LCD) device or camera, and a memory 101. The power supply IC 104 includes a power supply circuit (low dropout (LDO) regulator, DC-DC converter, or the like) 111 that stably outputs operation voltages of the respective devices.
Normally, power is supplied from a secondary battery 110 to the power supply IC 104. When a DC voltage 108 is applied from an external charger or the like to a charging IC 114, a voltage output from a DC-DC converter 109 of the charging IC 114 is supplied. Such paths are controlled by a charging control circuit 107 of the charging IC 114. A voltage is directly applied from the secondary battery 110, not via the power supply IC 104, to power amplifiers of a third-generation portable phone (3G PAs 105) and a power amplifier of a global system for mobile communications (GSM) portable phone (GSM PA 106), the 3G PAs 105 and the GSM PA 106 serving as devices that consume a relatively large amount of power.
In the existing configuration illustrated in FIG. 1, when the DC voltage 108 is applied, the charging control circuit 107 detects it and turns on a FET 112 (the FET 112 is connected), thereby starting charging of the secondary battery 110. At this time, when a current that can be supplied by the DC voltage 108 is smaller than the sum of a current supplied to devices connected to the power supply IC 104 and a current supplied to the 3G PAs 105 and the GSM PA 106, the charging control circuit 107 turns on a FET 113, switches a power supply path from the DC-DC converter 109 to the secondary battery 110, and stops output of the DC-DC converter 109 at the same time. The devices connected to the power supply IC 104 include the memory 101, the peripheral device 102, antenna switches (ANT SWs) 103, and the BB IC 100 in this example.